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As levels of carbon dioxide in the atmosphere rise in the 21st century, the nutritional value of many major food crops could decrease.

Max Taub, an associate professor of biology at Southwestern, did a “meta-analysis” of previous research that had been done on the effect of increased atmospheric carbon dioxide on the protein concentrations in barley, rice, wheat, soybean and potato.

His study found that the crops had significantly lower protein concentrations when grown in atmospheres containing elevated levels of carbon dioxide. Potatoes showed a nearly 14 percent decrease in protein, while the grain crops of barley, rice and wheat showed reductions of 15.3 percent, 9.9 percent and 9.8 percent respectively. The protein decrease in soybeans was much lower, at 1.4 percent.

“This is just one more example of the impact global changes could have on us,” Taub says. He notes that the impact will be felt the most in poorer countries, where people rely more on plant products for protein.

The study grew out of a question posed by a student in one of Taub’s Global Change Biology classes at Southwestern. Southwestern students Brian Miller ’07 and Holly Allen ’06, helped Taub analyze more than 200 experiments that had been previously conducted by other researchers. Their research has been accepted for publication in the March issue of Global Change Biology and is posted online at

Carbon dioxide levels in the atmosphere are rising, primarily as a result of the use of fossil fuels. Scientists estimate the current concentration of CO2 in the atmosphere is about 380 parts per million – up from about 280 parts per million before the industrial revolution began in the late 18th century. The concentration is expected to reach 540-958 parts per million by the year 2100.

As levels of carbon dioxide in the atmosphere rise, Taub explains, most plants show increased concentrations of carbon in their tissues and reduced concentrations of other elements including nitrogen, which is a key component of proteins. A certain group of plants known as C3 plants are most affected by changes in CO2 levels.

Taub estimates that 40 percent of human dietary protein worldwide comes from these so-called C3 grains and root crops, both of which show decreased protein concentration at higher levels of atmospheric carbon dioxide.

Taub notes that decreased levels of nitrogen in food crops could be partially overcome by the use of fertilizers containing nitrogen, but that could have other negative effects on the environment. Also, farmers in poor countries may not have access to chemical fertilizers. One possible option, he says, would be for farmers to breed grain varieties that have higher concentrations of proteins under conditions of increased CO2.

Taub is currently studying the impact of increased CO2 concentrations on the mineral composition of foods. Elements such as magnesium, potassium, calcium, iron and zinc are also important for a healthy diet.

Taub has been a member of the Southwestern faculty since 2001. He received his undergraduate degree in anthropology from the University of Massachusetts at Amherst and his Ph.D. in ecology and evolution from the State University of New York at Stony Brook.